1. Field of the Invention
The invention relates to a method for producing an inner contour on the inside wall of a workpiece with an internal arbor acting on the inside wall of the workpiece, which is cup-shaped or rotationally symmetrical. This method is especially useful for producing ring gears, slip bushings, ratchet bushings, couplers, or gear components provided in the same way with internal gearing. The workpieces are carried by a die that works together with the internal arbor during the cold forming.
2. The Prior Art
The production of rotationally symmetrical workpieces by cold forming is especially economical for highly stressed parts. To do this, an internal arbor whose circumferential surface corresponds to the internal profile after deformation is introduced into the formed part. On the one hand, this produces better strength characteristics resulting from material hardening and fiber structure during the deformation. On the other hand, the shape change necessary for the deformation is relatively slight, so that the work material retains sufficient toughness.
According to German Patent No. DE 199 10 474 A1, a hub sleeve is made by a rolling process or by a stamping process, in which the base part to be rolled does not undergo a length change. The deformation during the roller-pressing occurs principally in the radial direction. It is necessary to adapt the diameter ratios of the base part to the finished workpiece if the finished hub sleeve including the ball bearing race and knurl is to ensue without tilting the rolling of the tool.
To produce inside gearing for ratchet lock mechanisms, a negative impression of the gearing is machined into the profile on the internal arbor. The system shows an outer roller as a hollow cylinder with an internal profile, within which is located the internal arbor with its second profile, with the base part being roller-pressed by advancing against the outer roller. The advantage of the arrangement of an outer roller as a hollow cylinder with an internal arbor lies in the more stable rolling kinematics with a lengthened roller-pressing path, by which the base part is stabilized during the roller-pressing process and can be rolled without additional stabilizing aid.
Besides the rolling of teeth, the rolling of internal threads is known; it is carried out by rolling a rolling tool with a threaded roller. According to German Patent No. DE 40 34 795 C2, internal threads are produced in tubular workpieces with a tool with a helical working surface. The material is displaced from the thread base by the forming tool. With this method of deformation, very high pressures and frictional forces occur that increase sharply with increasing speed. This leads to rapid tool wear and to stripping of the threads on the workpiece. Rolling of internal threads requires a certain wall thickness and is thus unsuitable for sheet metal, for example.
For this reason, compression methods are used mainly when machining sheet metal workpieces, with the internal contour being imaged on a compression mandrel and the outer contour of the workpiece being imaged in a die. In German Patent No. DE 195 24 089 C1, a cup-shaped tool is used to produce a gear component with outer teeth. The metal blank rotating in the die is reduced in thickness with a compression roller by pressing from the center to the edge, and the material thus obtained is deformed to a cylindrical edge area projecting from the hub. The cylindrical edge area extending essentially perpendicular to the hub surface is provided with teeth on the outside.
In the production of an internally toothed gear component with a smooth outside according to DE 39 31 599 A1, a cup-shaped unmachined part is used that has been made either on a compression machine or a press. The unmachined part is located on a toothed compression mandrel and work is done on the rotating workpiece by means of a compression roller. In a first operating step, the workpiece is placed against the outer circumference of the compression mandrel provided with outside teeth, and in a second operating step the rotating cup-shaped workpiece is pressed by a compression roller into the grooves of the teeth, and is thereby lengthened at the same time.
The roller-pressing processes known from the state of the art for producing an inner contour have the drawback that the inner contour of the die is larger than the outer contour of the workpiece. The arbor roller for rolling the inner contour is substantially smaller than the inner contour of the workpiece. The rolling of the internal profiles is therefore associated with expansion of the unmachined part, which is disadvantageous for exact reproduction of gearing. When the rolling arbor and the die are driven at the same time, both have to have the same circumferential speed in the contact area with the workpiece. Also, material flow in the axial direction can be distinguished during the profile rolling, by which the workpiece becomes longer during the rolling, during the rolling process, corresponding to the volume of material displaced by the tool profile. When fabricating rings with large and deep profiles in gear rings or ratchet bushings, this leads to problems with the desired accuracy.